This is a continuation of International Application No. PCT/EP01/02795, with an International filing date of Mar. 13, 2001, published in German under PCT Article 21(2) which is incorporated herein by reference in its entirety and for all purposes.
The present invention relates to a deep-drawing method, with which a drawn part is arranged in a deep-drawing die between a first deep-drawing die part and a second deep-drawing die part and is formed by way of relative movement of the deep-drawing die parts in relation to one another.
Such deep-drawing methods are known from the state of the art.
In particular, deep-drawing methods with rigid deep-drawing die parts are known, with which the drawn part is drawn by a drawing punch into a drawing member (also called a female die), wherein the edge of the drawn part can be held securely by means of a drawing ring.
In order to achieve the desired, final configuration of the drawn part, it is often necessary to form the drawn part in several consecutive drawing processes (also called operations).
In this respect, there is, however, the problem that the structure of the material of the drawn part will be solidified during the first drawing process such that it no longer has sufficient fluidity for an additional drawing process which can lead to the formation of cracks during the additional drawing process.
If the material of the drawn part is steel, martensite is formed, in particular, during the first drawing process and this reduces the formability of the drawn part during an additional deep-drawing process.
In the case of the known, multiple operation deep-drawing methods, the required formability of the drawn part is therefore established again following the first deep-drawing process in that the drawn part is annealed at a temperature of approximately 1050xc2x0 C., wherein the martensite, in particular, which has been formed during the first deep-drawing process, is converted into austenite which can be formed more easily.
If more than two deep-drawing processes follow one another, the annealing of the drawn part will possibly have to be repeated after each deep-drawing process.
On account of the annealing, cooling and washing processes required prior to each additional drawing process, the known, multiple operation deep-drawing methods require considerable time and energy.
It is therefore an object of the present invention to provide a deep-drawing method of the type described at the outset whichxe2x80x94particularly when carrying out several consecutive drawing processesxe2x80x94is more time- and energy-saving than the known deep-drawing methods.
The present invention relates, in addition, to a deep-drawing die, comprising a first deep-drawing die part and a second deep-drawing die part, in which a drawn part can be formed by way of relative movement of the deep-drawing die parts in relation to one another.
A further object underlying the present invention is to provide such a deep-drawing die, with the aid of which drawn partsxe2x80x94in particular within the scope of a multiple operation deep-drawing methodxe2x80x94can be formed in a more time- and energy-saving manner than with known deep-drawing dies.
These objects are accomplished in accordance with the invention, in a deep-drawing method using cooperating deep-drawing die parts, in that a pressure variable with time during the drawing process is generated selectively at a limited pressure section of one of the deep-drawing die parts, this pressure pressing a section of the drawn part, which abuts on the pressure section, against the other deep-drawing die part.
The idea underlying the inventive solution is to achieve a flow of the material of the drawn part sufficient for its forming by concertedly acting upon a limited area of the drawn part during the drawing process even when the flowability of the material of the drawn part is reduced as such on account of the previous history of the material, for example on account of a preceding, earlier drawing process.
The desired formability of the drawn part can be ensured, in particular, with the inventive deep-drawing method even when the drawn part contains martensite on account of a preceding drawing process.
An annealing process and the cooling and washing processes associated with the annealing process may be omitted in the case of the inventive deep-drawing method even when the deep-drawing method is carried out in several operations.
The inventive deep-drawing method allows a particularly large drawing ratio to be achieved and leads to a high form stability of the drawn parts.
In a preferred development of the inventive method it is provided for the pressure at the pressure section to be generated hydraulically or pneumatically by means of a pressure fluid.
The hydraulic generation of a pressure at one of the deep-drawing die parts is already known as such from the so-called hydroforming method, with which the drawing member is provided with a membrane which is subjected to water pressure during the forming process. With this method, the drawing punch presses the drawn part against the membrane on the drawing member, wherein the drawn part is formed by the water pressure acting against it. With this method, the entire drawn part is, however, subjected to the same water pressure during the drawing process whereas, in the inventive deep-drawing method, a pressure is generated selectively only at a limited pressure section of one of the deep-drawing die parts and this pressure presses the respective limited section of the drawn part, which abuts on the pressure section, against the respectively other deep-drawing die part.
Moreover, in the case of the hydroforming method the water pressure acting on the drawn part is constant during the drawing process.
One variation of the hydroforming method is the so-called hydro-mec method, with which the drawn part is pressed by a descending drawing punch into water subjected to pressure without a membrane being provided on the drawing member. With this method, as well, no selective action on a limited section of the drawn part with a pressure variable with time during the drawing process is provided.
A uniform distribution of the hydraulic pressure on the surface of the drawn part is the aim not only of the hydroforming method but also of the hydro-mec method and this is completely contrary to the inventive idea of acting upon a limited section of the drawn part selectively with an increased pressure.
In a preferred development of the inventive deep-drawing method it is provided for the pressure at the pressure section to be controlled and/or regulated in accordance with a predetermined temporal pressure course.
This pressure course may provide, for example, for the pressure section to be switched to a no-pressure state during a first forming phase and for an increased pressure constant throughout a second forming phase to be generated at the pressure section during the second forming phase. Such a pressure course can be controlled and/or regulated particularly simply.
However, any optional, other temporal pressure course can also be controlled and/or regulated depending on the type of drawn part and the desired forming of the drawn part.
The formability of the drawn part during the drawing process is particularly increased when the pressure section is aligned essentially parallel to the direction of drawing, along which the deep-drawing die parts are moved relative to one another. In this case, areas of the drawn part which are aligned essentially parallel to the direction of drawing can be pressed concertedly onto areas of the respectively other deep-drawing die part which are aligned essentially parallel to the direction of drawing, and this is not possible in the case of the conventional deep-drawing methods. Side wall areas of the drawn part, which are aligned essentially parallel to the direction of drawing, can, in particular, be formed in a particularly exact manner.
The inventive deep-drawing method has proven to be particularly successful when the side wall of the drawn part is exclusively acted upon during the drawing process with the pressure variable with time at the pressure section. Such a deep-drawing method is particularly suitable for the production of Gastronorm food containers which have a great depth and tend to form undesired bulges in the side wall area which can lead to a poor stacking capability of the food containers. Such bulging can be prevented or any bulge generated during a preceding deep-drawing process eliminated as a result of the concerted action on the side wall of the Gastronorm food container during the drawing process with the pressure variable with time at the pressure section.
In a preferred development of the inventive deep-drawing method it is provided for the pressure section to be of a ring-shaped design.
No further details have so far been given as to how the pressure variable with time is generated at the pressure section.
It may be provided for the pressure variable with time to be generated by means of a pressure generating device which comprises a chamber for accommodating a pressure fluid subject to pressure and an elastically deformable chamber wall for transferring the pressure from the pressure fluid to the drawn part.
Such a chamber may, in particular, be of a ring-shaped design.
Such a chamber is particularly easy to produce when it is limited partially by the elastically deformable chamber wall and partially by a chamber limiting wall consisting of a material different from the material of the elastically deformable chamber wall, preferably consisting of a metallic material, in particular, aluminum.
In principle, the pressure section may be arranged on the first deep-drawing die part or on the second deep-drawing die part. Furthermore, it may be provided for not only the first deep-drawing die part but also the second deep-drawing die part to each have one or more pressure sections, at which a respective pressure variable with time is generated during the drawing process.
In a preferred development of the inventive deep-drawing method it is provided for the first deep-drawing die part to be designed as a drawing member and the second deep-drawing die part as a drawing punch and for the pressure section to be arranged on the drawing member.
In principle, the relative movement between the drawing punch and the drawing member required for forming the drawn part may be generated not only by a movement of the drawing punch but also a movement of the drawing member or also by a movement of both deep-drawing die parts.
In a preferred development of the inventive deep-drawing method it is provided for the drawing punch to be stationary during the drawing process and the drawing member to be moved towards the drawing punch.
As already explained, the inventive deep-drawing method is particularly advantageous when the drawn part is preformed during a first drawing process and postformed during a second drawing process, during which the pressure variable with time is generated at the pressure section. In this case, the annealing required with the known deep-drawing methods and the cooling and washing processes necessary as a result prior to the second drawing process can be dispensed with, which results in a considerable saving on time and energy.
The two drawing processes may be carried out in the same deep-drawing die, wherein it is normally necessary to change the deep-drawing die parts between the drawing processes, or the two drawing processes are carried out in different deep-drawing dies, which is recommended for a series production since, in this case, the deep-drawing die parts required for the respective drawing process can remain in the respective deep-drawing die.
The further object is accomplished in accordance with the invention in that one of the deep-drawing die parts has a limited pressure section, at which a pressure variable with time can be generated selectively during the drawing process, this pressure pressing a section of the drawn part which abuts on the pressure section against the respectively other deep-drawing die part.
The advantages of the inventive deep-drawing die have already been explained above in conjunction with the inventive deep-drawing method.